Oracle eyes optical links as final frontier of data-center scaling

Oracle is exploring silicon photonics, an optical technology drawing widespread interest, as a potential weapon in the battle against data-center power consumption.

Advances in CPU and memory design could boost efficiency dramatically over the next few years. When they do, the interconnects among components, servers and switches will effectively become the power hogs of the data center, according to Ashok Krishnamoorthy, architect and chief technologist in photonics at Oracle.

Optical connections, which will eventually be needed for high-speed links within rows and racks of servers, promise efficiency gains over copper cables but need to get cheaper first. A key part of that effort will be integration, the time-honored work of bringing the functions of many separate chips into one. Silicon photonics is a likely technology for doing that, though it probably won't ship in volume for two years or so, said Linley Group analyst Jag Bolaria.

Oracle isn't often associated with networking and may not even manufacture or sell the technologies it's now studying. But as a big player in computing and storage, it could benefit from fostering a future technology that helps make faster, more efficient data centers possible.

Like other Oracle hardware divisions, the photonics unit has its roots in the former Sun Microsystems, which began work on short-reach optical communications in 2004 and has had a photonics partnership with the U.S. military research agency DARPA since 2008. Silicon photonics is part of Oracle's larger effort to help data centers and private and public clouds meet future computing needs, Krishnamoorthy said.

"We see bandwidth and computing demand growing unabated," he told an audience at the recent Open Server Summit in Santa Clara, California. "Can we scale infrastructure and systems to meet demand?"

Silicon photonics holds the potential to help do that, Krishnamoorthy said. In his conference presentation, he used power consumption as a measure of efficiency, while adding that space and cooling are also critical issues.

Work that the industry is already doing may make both CPUs and memory several times more efficient over the next several years, Krishnamoorthy said. At that point, connectivity will consume a much bigger percentage of a data center's power than it does now. "If we do our job here, then we have sort of this gaping interconnect problem," he said. Oracle's goal is optical interconnects that use about one-tenth as much power as those in use now.

For high speeds over long distances, optical links are already standard. Multi-gigabit carrier backbones can carry a whole city's data as waves of light, which are converted to and from electrical signals on each end. When individual servers start generating enough information, data-center architects will have to use optical technology just to connect them the top of the server rack.

We're not there yet. Even at 100Gbps, electrical interconnects can go four or five meters, enough to reach the top of a rack of servers, Linley Group's Bolaria said. And even though the need for 100-Gigabit links is starting to creep into the busiest data centers, there's still room to grow because those connections are really made up of four 25Gbps wires, he said.

But Krishnamoorthy sees a transition to optics coming. "We think that the speeds at 25-gigabit and beyond will get us to push optics onto every blade," he said.

Ultimately, Oracle wants to take photonics even beyond server interfaces. Miniaturized connections could link processors at high speed across a motherboard, Krishnamoorthy believes.

The current high cost of optical modules isn't as important for long-distance network interfaces as it is for server connections, because there are relatively few of them, according to Bolaria. But when every server needs an optical connection to a top-of-rack switch, data-center builders will need something both less expensive and smaller than a module with multiple parts to it, and that's where silicon photonics comes in, he said. Though other chip-making materials are used today in some highly integrated optical interfaces, silicon is likely to win out because of the huge industry already in place around silicon, Bolaria said.

Oracle is in good company. In addition to startups such as Luxtera, big names are pursuing silicon photonics. Cisco Systems recently acquired silicon photonics startup Lightwire, and data-center interconnect vendor Mellanox Technologies has bought another new player, Kotura. Intel is also developing data-center photonics, including through a collaboration with Facebook.

Though it's not needed yet, they're all thinking ahead, Bolaria said.

"At some point, electrical will fail to suffice for what we're trying to do," he said. "It's going to take years, so a lot of them are spending money in it now so they can be better prepared than their competitors when that happens."

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